Vision aid devices which are worn on the head are typically located directly in front of the aided eye or eyes. As these systems migrate from direct view optical paths to digital camera aids, the system configuration requires that a head mounted display (HMD) be placed directly in front of the user's aided eye, with one inch of eye relief. This placement of the HMD prevents the co-location of the camera aperture directly in front of the aided eye. The camera aperture must be moved either in front of the HMD or to one side of the HMD.
If, for example, the digital camera is placed 100 mm to the side of the optical axis of the aided eye, then a displacement is created between the aperture of the digital camera and the image display of the digital camera, the display typically centered about the optical axis of the aided eye. This displacement creates a disparity between the apparent positions of objects viewed through the camera, and the actual positions of the objects seen in object space (or real space). This offset in perceived space and object space is referred to as parallax.
FIG. 1 provides an example of parallax error. As shown, the user is viewing environment 10 through a head mounted video device. The user sees tool 12 at close range and attempts to pick up the tool. Because of parallax, the perceived position of tool 12 is incorrect. The true position of tool 12 in object space is shown by dotted tool 14.
In the case of the user viewing an object through a head mounted video device, parallax reduces the usefulness of the video system. The human psycho-visual system is unconsciously attuned to perceiving the world through its natural entrance aperture, which is the pupil in the human eye. The hand-to-eye coordination inherent in manual tasks is based on this innate property. Normal human movement tasks, such as walking and running, depend on this subconscious process. A fixed system, which is aligned to remove parallax at some fixed distance, is miss-aligned at all other distances. This is especially true when the video system is aligned to remove parallax of an object at far range and the user attempts to locate another object at close range, such as tool 12 on FIG. 1 which is located within an arms length of the user.
As will be explained, the present invention addresses the parallax problem by providing a system for dynamically realigning the video image so that the image coincides with the real world at all distances.